Method for imparting color to cedarwood



of water absorption.

United States PatentOfitice 2,940,811 Patented June 14-, 1960 METHQD FOR EIPARTENG COLOR TO CEDARWOGD Eduard Far-her, Washington, D.C., assignor, by mesue assignments, to Great Western Producers, Inc, Gulf Red Cedar Company Division, New York, N.Y., a corporation of Maryland No Drawing. Filed Get. 6, 1959, Ser. No. 344,622

16 Claims. (Cl. 8-6.5)

This invention relates to the preparation of cedarwood for the manufacture of pencils. More particularly, the invention relates to a novel process effective to impart a reddish color to the heart and sapwood of incense cedar.

It is conventional practice in the prior art to treat cedarwood from which pencils are manufactured to impart thereto a generally uniform reddish color by impregnation of cedar slats with a solution of an appropriate dye, normally an azo-dyestui'f. More specifically, in accordance with such prior art processes, cedar slats are moved through pressure vessels containing a dyestufi solution. Vacuum and superatmospheric pressure conditions are required to efiect saturation by impregnation of the cedarwood slats with the dyestuff solution. During the period of residence in the pressure vessels, normally at least about a few hours, the cedarwood slats increase in weight about 150% to 200% by reason primarily Water so absorbed must be removed over a long period of time in a carefully regulated, drying operation which normally requires from about ten to about fourteen days, and necessitates the maintenance of a large inventory of pencil slats in process.

It is accordingly a primary object of this invention to provide an improved method for imparting a satisfactory red coloration to cedarwood pencil slats.

It is a more specific object of the invention to provide a. method for the production of a satisfactory red color in cedar-wood slats which does not require the utilization of vacuum or superatmospheric pressure conditions.

It is an additional object of the invention to provide a process for imparting a satisfactory color to cedar pencil slats pursuant to which treated slats can be etfectively dried without material adverse efiect a substantially shorter time period than is required by prior art methods.

It is yet a further object of the invention to provide an economical method for imparting a satisfactory red color cedar-wood pencil slats which can be completed in a materially shorter period of time than conventional processes for achieving a like result.

A more specific object of the present invention to provide a process pursuant to which an alkali metal nitrite and a dyestufi are used in conjunction to impart a color to cedarwood appropriate for use in pencil manufacture.

It is an additional object of the invention to provide an effective two-stage process for imparting an appropriate reddish coloration to cedarwood pencil slats pursuant to which a dyestuff is so employed as to obviate the timeconsuming impregnation procedures essential to prior art cxpedients entailing dyestuff utilization.

In accordance with this invention, it has been discovered that a. reddish coloration satisfactory for pencil manufacture can be imparted to cedarwood by contacting said cedarwood with an aqueous solution containing from about 1% to about 6% by weight of an alkali metal nitrite under conditions to effect absorption by said wood of from about 0.03% to about 5.0% .by weight of said nitrite and thereafter gradually removing water from the nitrite-containing wood over a time period of at least about twelve hours to produce a colored cedarwood prodnot containing not more than about 10% water.

In accordance with a more specific aspect of the invention, it has been discovered that a red coloration satisfactory for pencil manufacture can be impaired to cedarwood by a process which comprises first contacting cedarwood with an aqueous solution containing from about 1% to about 6% by weight of an alkali metal nitrite and thereafter contacting said cedarwood with an aqueous solution of a dyestuff of appropriate coloration, said cedar-wood absorbing in said process from about 0.03% to about 5.0% by Weight of alkali metal nitrite, and thereafter gradually removing water from the nitritecontaining cedarwood over a period of at least about 1Q hours to produce a colored cedarwood product containing not more than about 10% by weight of water.

Pursuant to the invention, aqueous solutions of all alkali metal nitrites can be employed, including specifically sodium, potassium and lithium nitrite. Sodium nitrite is preferred. The aqueous alkali metal nitrite solutions utilized normally do not contain more than about 6% by weight of nitrite to foreclose the formation of an undesired dark color in the outer layers of the cedarwood treated. In the practice of the invention to produce a product in which such darker colors are not disadvantageous, alkali metal nitrite concentrations in excess of 6% by weight can be utilized. A practical lower limit of nitrite concentration is about 0.1% by weight. Preferably, alkali metal nitrite solutions containing from about 3% to about 5% by weight of alkali metal nitrite are employed.

The process of the invention is appropriately practiced at atmospheric temperature, normally about 20 C., although any temperatures between the freezing and boiling points of the aqueous treating solution can be employed. A temperature range of from about 60 C. to about 90' C. is preferred.

Atmospheric pressure is preferable in the practice of the invention. Utilization of superatmospheric pressure or subatmospheric pressure or a combination thereof to facilitate impregnation of the slats with the treating solution in conventional manner is not precluded but is not essential to the success of the invention.

Cedarwood undergoing treatment in accordance with the invention is maintained in contact with the treating solution for a period of time requisite to provide a concentration of nitrite in the wood within the range of from weight of alkali metal nitrite are employed, the total quantity of the solution absorbed by the wood will vary from about 30% to about preferably from about 40% to about 60%, by weight of the wood.

The cedarwood should not remain in contact with the treating solution for more than about one hour to minimize the possibility of adverse effect on the color. of the final product. Prolonged treatment, particularly at elevated temperatures, reduces the natural color of theheartwood. It is, accordingly, preferred to complete the treatment within a period of not more than about 60 minutes. Treating periods of about twenty minutcst or less are frequentlyadequate.

To facilitate and expedite the absorption of the treating solution by the wood, it is preferable to varythe treating temperature during the contact period. Accordingly, a preferred embodiment ofthe invention entails stage product is contacted with a treating solution substantially cooler, preferably at least about 10' C., than the first stage solution for a period of not more than about 15 minutes, preferably from. about 2.to about 10 minutes; The second stage treating solution is employed at a temperature of not more than about 80 C., pref- -erably from about 20 C. to about 40 C.

It will be appreciated that in accordance with the twostage method of practicing the invention, the concentrations of the treating solutions in the respective stages can appropriately be'varied. Normally,'a more concentrated solution is employed in the first stage. For example, it

is'appropriate to use a. relatively concentrated solution containing from about 4% to about 6% by weight of an alkali metal nitrite in the first or high temperature stage, "and a more dilute solution containing from about 1% to about 3% or. 4% by weight of alkali metal nitrite in the :secondor low temperature stage.

Water is removed from cedarwood treated injaccordance with the invention over a period of at least about 12 'hours tofacilitate uniform distribution of thealkali metal nitrite in the wood while the wood is wet and to preclude accumulation of the nitrite close to the wood surface. Water removal is eflt'ected in this manner to produce]; colored cedarwood product which contains not more than about and preferably from about 5% to about 10%,

:by weight of water. A layer of darkened wood of un- '-satis'factory color may be produced, particularly when". the more concentrated solutions containing 5% or more by'weight of alkali metal nitrite are employed.

9? The production "ofsuch disadvantageous darkening il foreclosed by th e two-stage process in which the second stage of impregnationis effected at-a'relatively low ternperature with a nitrite solution of lower. concentration.

Alternatively; such disadvantages darkened layers can be avoided by rinsing the single stage treated 'cedarwood with water. A relatively fast dip in warm water is ade- '-quate.

ducethedesired color. I

' In that embodiment of the process of the invention in i which a dyestufi' is employed after nitrite treatment, at-

imolpheric temperatures and pressures are also approxi- V mately utilized, although all temperatures within the rangebetween the freezing point of the dyestufi solution and the boiling point thereof can be employed. Subatmospheric of superatmospheric pressure conditions or combinations thereof are not essential but-can be employedlin conventional manner to facilitate the absorption of the dyestufiby the wood. 7 I

In accordance with the'modification of theinvention, in which a two-step alkali metal nitrite impregnation proceu is used in the first stage, the dyestufi can be added to the alkali metal nitrite solution utilized in the second 7 step. Such a mode of operation is, however, not pretenedby reason of the adverse effect of the 'dyestufl in the absorption in formation of color in the wood. 7 Any appropriate dyestutf. can be utilized, n'ormally in a concentration of from about $4 of one part by weight to about 70 to 200 parts by weight of the aqueous solu- -tion. Re presentative dyestuifs whichmay be suitably employed are aniline, quinoline and 'anthraquinone dyestuffs. More specifically, Napthol Yellow S, Ponceau, Methyl -Violet, natural dyestufis including logwood and indigo and the likeare contemplated. Appropriate azo dyesare listed at pages 261 to 293,,appropriate anthraquinone dies .atpages 343' to 350, appropriate aniline dyes at pages 337 and appropriate quinoline :dyes at page 328. of Gilman,

JOrganic Chemistry, an Advanced Treatise]? Reference is made to The Chemical Formulary," vol. IV, page 34 6 (1939), and vol. V, page 284, Chemical Publishing Co., Inc., for the disclosure of wood dyeing techniques. Smith Patent 2,713,364 and German Patents 422,124 and 439,226 also describe wood dyeing processes, and dyes useful therein.

' Example I A group of approximately 100 dried, incense cedar, about 2%" x x 7%" pencil slats weighing about 515 lbs. was immersed in a water solution containing about 2% by weight of sodium nitrite and maintained at a temperature of about 85 C. for a period of about fifteen minutes. Atthe termination of the first fifteen minute period, the treating solution containing the slats was cooled during an additional fifteen minute period to about 60' C. The slots were maintained immcrsedin the 60 C. solution for a third fifteen minute period and then re moved. The heated slats reflected a weight increase of about 47% of the original weightthereof by reason of- .the absorption of the treating solution. The treated slats were then maintained in a confined space with air circulation for a period of about eight hours and thereafter exposed to drying conditions in a stream of warm air characterized by a temperature within the range of about 50 C. to about 75 C. After about five day under such drying conditions, it was found that the moisture content of the treated slats is reduced to from about 5% to about 10% .by weight, and that a satisfactory red color for the production of pencils'had developed in the V slats.

Byway of comparison, similar slats treated identically, with the exception that the treated slats were dried rapidly over aperiod of only about six hours to a moisture content of from about 5% to about 10% by, weight, developed only slight coloration andwere unsatisfactory for the manufacture of pencils. 7

Example 11 Cedsrwood slats of the same type and in the same amount as described in Example I wereimmersed in a 5% by weight water solution of sodium nitrite at a temperature of 90 C. for a period of ten minutes, removed from the 5% treating solution, and thereafter immersed in a like solution containing only about 1% by weight of sodium nitrite at a temperature of about 40 C. The slats so processed were dried slowly'in the same manner as described in Example I. A uniform red'color satisfactory for the manufacture of pencils developed in the treated slats. r

' Example III those described in Example' I were immersed in a water solution containing 4% by weight of sodium nitrite and 2% by weight of urea maintained at a temperature of 70 C. After ten minutes of such immersion, the slatsincreased in weightby 26% and were thereafter immersed in a solution containing 2% sodium nitrite and 1% urea at a temperature of 30 C. for a period of about fifteen minutes. The slatsremovedfrom the second treating solution were found to weight 48% more than the original untreated slats. After slow drying in the manner de scribed in Example I, the treated slats were found to be uniformly colored red in 'a manner satisfactory for the Example IV A group of cedar slats identical with those described in Example I are immersed in the first stage in a water solution containing 4%.by weight of sodium nitrite and 3% by weight of urea maintained at a' temperature of 75 C. for a period of thirty minutes. The slats were then re- :moved from the firststage treating solution and immersed in a water solution containing 2% by weight of paraflin in semen a emulsion maintained at a temperature of 30 C. for fifteen minutes.

After removal from the second treating solution and drying in the manner described in Example I, the cedar slats were found to be appropriately colored red and suitable for use in the manufacture of pencils.

It will be appreciated that softening agents other than urea and parafiin emulsions such as polyethylene glycols, invert sugar, and the like, can be employed in conjunction with the alkali metal nitrite treating solutions of the invention to produce a desirable degree of softness in the treated cedarwood product. For example, water solutions containing from about 2 to about parts, preferably about 4 parts, by weight of alkali metal nitrite and from about 1 to about 3 parts, preferably about 2 parts, by weight of polyethylene glycol having an average molecular weight of about 200 can be employed. Similarly, a water solution containing from about 2 to about 5 parts, preferably about 4 parts, by weight of alkali metal nitrite and about 3 to about 6 parts, preferably about 4 parts, by weight, of invert sugar can be employed. In general, the range of concentrations of such softening agents in the treating solutions of the invention is from about 2% to about 5% by weight.

A further specific embodiment of the invention contemplates the utilization of resorcinol in conjunction with an alkali metal nitrite in the production of a satisfactory reddish coloration in cedarwood pencil slats. In accordance with such embodiment of the invention, resorcinol is employed in the aqueous alkali metal nitrite treating solutions, preferably in proporitions of from about 0.1% to about 3% by weight. The resorcinol is employed either in the one-stage or in the two-stage mode of practicing the invention. When utilized in the two-stage method, the resorcinol is appropriately employed solely in the first stage, solely in the second stage, or jointly in both stages.

The following example is illustrative of the practice of the invention utilizing resorcinol.

Example V Cedarwood slats, of the same type and in the same number as described in Example I, are immersed for about 40 minutes in a water solution containing about 1% by Weight of sodium nitrite and about 1.6% by weight of resorcinol, maintained at a temperature of about 80 C. The solution containing the cedarwood slats is then coled to about 50 C. and the slats are maintained immersed in the 50 C. solution for about additional minutes. The slats, upon removal from the treating solution, are found to have absorbed about 70% by weight thereof and are satisfactorily colored after drying in the manner described in Example I.

Example VI A group of 100 incense cedar slats containing about 7% moisture, about 2 /8" x x 1%" in dimension, and weighing 2652 grams were immediately immersed in a 5% water solution sodium nitrite maintained at 70 C. for about 30 minutes. The treated slats upon removal from the treating solution weighed 3476 grams and were immediately immersed in a water solution of 0.07% by weight of a commercial azo-dyestutf maintained at a temperature of about 40 C. for a period of about five minutes. The dyestufi employed was a sulfonate. The weight of the slats upon removal after five minutes immersion in the dyestufl" solution was 3953 grams. The treated slats were then dried by subjection to a temperature of about 75 C. for twelve hours in a humid atmosphere during which time only slight evaporation of water took place, followed by exposure to drying took place, followed by exposure to drying conditions in a stream of warm air characterized by a temperature within the range of about 50 C. to about 75 C. for a period of about 2 days to produce a final, dried, colored 13 product containing about 7% by weight of water and appropriately colored both intern-ally and externally for the manufacture of pencils.

Example VI] A group of slats, similar to that described in reference to Example VI, was immersed in a water solution containing 4% by weight of sodium nitrite for ten minutes at 90 C at atmospheric pressure. The slats were then removed from the sodium nitrite treating solution and immersed in a solution containing 1% by weight of sodium nitrite and 0.1% by weight of the same azo-dyestuff described in Example VI. The slats were removed from the second treating solution after about ten minutes at a temperature of about 50 C. Thetreated slats reflected a Weight increase of about 55%. The slats so produced were dried in the same manner as the slats in Example VI to produce a similar product.

Example VIII A group of slats of incense cedar, of the same type described in Example VI were immersed in atmospheric pressure in a 4% solution of sodium nitrite maintained at a temperature of about 90 C. After immersion for ten minutes, the treating solution was cooled to about C. and the slats were removed therefrom. It was determined that the slats had increased in weight by 36% by reason of absorption of the treating solution.

By way of comparison, an identical process was repeated with the exception that the treating solution con by weight of sodium nitrite,"

dyestufi is employed, demonstrated very little coloration of the Wood, although the surface of the slats was adequately colored.

Example IX Example VII is repeated with the exception that the dyestutf solution employed in the second stage contained 2.5% by weight paraffin in emulsified form. The dried product produced was characterized by an enhanced softness appropriate for pencil manufacture. The quantity of dyestuff absorbed on the cedarwood surface corresponded to about 0.03% by weight of the cedarwood. In prior art procedures entailing the utilization of vacuum and pressure for eifecting the coloring of cedarwood slats of dyestufis, at least about 0.2% by weight of dyestufit' is consumed.

It will be appreciated that other softening agents and parafin emulsions, such as polyethylene glycols, invert sugars, and the like, can be employed in either stage of the process of the invention to produce a desirable degree of softness in the colored cedarwood product. For example, treating solutions containing from about 2 to about 5, preferably about 4, parts by weight of alkali metal nitrite, and from about 1 to about 3, preferably about 2 parts, by weight of polyethylene glycol having an average molecular weight of about 200 can be employed in the first stage. A like amount of polyethylene glycol can be employed in the second stage. Similarly, a water solution containing from about 2 to about 5, preferably about 4, parts by weight of alkali metal nitrite and about 3 to about 6, preferably about 4, parts by weight of invert sugar can be employed in the first stage. Corresponding amounts of invert sugar can be employed in the second stage. In general, the range of concentraabandoned. a

'I claim: 1; The process for imparting a reddish coloration satisfactory forpencil-manufacture to cedarwood slats which comprises, contacting said cedarwood with an aqueous solution= containing from: about 1% to'about 6% by weight of an alkali metal. nitrite under-conditions to effect absorption bysaid wood of from about 0.03% to about *.O% -by-weight of said nitrite and thereafter gradually removing water from the nitr-ite containing produce a colored 'cedarwood product containing not more than about water.

2. The process of claim 1 wherein the alkali metal nitrite is sodium nitrite.

- 3. The process of claim l carried out at a temperature of from. about 60 C. to-about 90 C.

i 4.- Theprocess ofv claim 1- wherein said alkali metal nitrite solutionv contains: from about 3% --to' about'5%" by weight of alkali metal. nitrite. V

5. The processof claim 1 'wherein'said alkali metal nitrite treatingx-solution contains a. softening agent selected from the .group consisting of urea, aqueous emulsions of parafiin wax finelydispersedthrough emul-- sifying agents, polyethylene glycols, and. invert sugar.

6. The process of; claim 1 wherein saidaqueous solution of analkali metal nitrite contains from about 0. 1%

a to about 3% by'weightof resorcinal.

' 7. The process. for imparting a reddish. coloration satisfactory forpencilmanufacture to cedarwood which comprises a first stage, in which the cedarwood iszcontacted with an aqueous solution ofran alkali metal nitrite containing from about 4% to;about 6% by weight of alkali metal nitrite at a temperature in excess of. about 50, C. for a period of not more than about 60 minutes,:

and a second stage in which the'first stage product-sis contacted with an aqueous solution of an alkali metal nitrite at least about 10 C. cooler than the first stage' treating solution and containing'from about 1% to about 3% by weight of alkali metal nitrite for a period of .not more than aboutv minutes.

j 8. The process of claim 7 wherein said second stage treatingsolution is employed at a temperatureiof from about 20C. to about C. a V 9; The. process of claim 7 wherein at leastrone-ofjsaid first stage and second. stage. treating solutions contain from about 0.1% to about"3% by weighfofresorcinol.

10. A process for imparting a red colorationsatisfactory for pencil manufacture .tocedarwoodacomprising a first stage (11) in which awcedarwood is-contact'ed with an aqueous solution containing from:.'ab'out.1%; to about 6% by weight-of analkali metal nitrite,,and aisccond wood over a time period of atleast about 12 hours to stage (1)) .in which the first stage product. is contacted with an aqueous solution of. a: dyestufinfappropriate coloration for dyeing cedarwood, said cedarwood absorbing ins'aidprocess. from about 0.03 toabout 5.0% by weight of alkalifmetal. nitrite, and thereafter gradually removing water from the nitrite-containing cedarwood over a period of at least about 12 hours to produce a colored cedarwood product containing not more than about 10%: by weight of water.

11.- The processor claim 10. wherein said first, stage (;a)- and said second stage'(b);are practiced at substantially' atmospheric; pressure.

12. The process of claim 10 wherein. said first stage (a) is carriedout in two steps, including a first step in which an alkali metal nitrite. solution containing from about 4% to about 6% by weight of alkali metal n-itrite is'employed, and a second step in which from about 1% to about 4% by weight of alkalimetal nitrite is employed. v V

v 13. The process of claim 12 wherein said first step is practiced at a temperature of from about C. to about C., and wherein said second step is practiced at a temperature at least, about ten degrees lower than said first step. 7

14. The process of claim 10 wl1erein there is-employed in saidsecond stage, (-b) ;an QQUtIOUS SOlLlilOILOf a ,dyestuii .containing,-in addition to said dyestutf, from about l%- .to abou t 3% by weight of an alkali metal nitrite. 15. Cedarwood colored in accordance with the method of claim 10. I g

16. The process of claim 10 wherein said aqueous solution contains a softening agent" selected .from the group consisting of urea; polyethylene glycols, invert 40' sugars and aqueous emulsions offparaflin wax finely dispersed through emulsifying agents.

, References'Citefi in the file of this patent iv I "UNITED STATES "PATENTS a Great Britain se t. 6,1928 

1. THE PROCESS FOR IMPARTING A REDDISH COLORATION SATISFACTORY FOR PENCIL MANUFACTURE TO CEDARWOOD SALTS WHICH COMPRISES, CONTACTING SAID CEDARWOOD WITH AN AQUEOUS SOLUTION CONTAINING FROM ABOUT 1% TO ABOUT 6% BY WEIGHT OF AN ALKALI METAL NITRITE UNDER CONDITIONS TO EFFECT ABSORPTION BY SAID WOOD OF FROM ABOUT 0.03% TO ABOUT 5.0% BY WEIGHT OF SAID NITRITE AND THEREAFTER GRADUALLY REMOVING WATER FROM THE NITRITE-CONTAINING WOOD OVER A TIME PERIOD OF AT LEAST ABOUT 12 HOURS TO PRODUCE A COLORED CEDARWOOD PRODUCT CONTAINING NOT MORE THAN ABOUT 10% WATER. 